1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor, a display device including the semiconductor device, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, liquid crystal display devices typified by liquid crystal displays are becoming widespread. As liquid crystal displays, active matrix liquid crystal display devices where pixels are each provided with a thin film transistor (TFT) are often used. In thin film transistors included in an active matrix liquid crystal display device, amorphous silicon or polycrystalline silicon is used for an active layer. A thin film transistor including amorphous silicon has low field effect mobility, but can be easily formed over a large-sized substrate such as a large glass substrate. On the other hand, a thin film transistor using polycrystalline silicon has high field effect mobility, but needs a crystallization process such as laser annealing and takes an enormous amount of time to be formed over a large-sized substrate such as a large glass substrate.
In view of the foregoing, techniques in which a thin film transistor is manufactured using an oxide semiconductor instead of the above silicon material and applied to electronic devices or optical devices have attracted attention. For example, Patent Document 1 and Patent Document 2 disclose a technique in which a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as an oxide semiconductor film and such a transistor is used for a switching element or the like of an image display device.